[Bug c++/109997] __is_assignable(int, IncompleteType) should be rejected

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109997

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Looks pretty similar, although I don't think we even had __is_assignable when
that was filed.